Process for recovering alcohol

ABSTRACT

Recovery of an alcohol such as ethanol from a crude alcohol product, preferably obtained from the hydrogenation of acetic acid using a low energy process. The crude ethanol product is separated in a column to produce a distillate stream comprising ethyl acetate and a residue stream comprising ethanol, acetic acid, and water. The ethanol product is recovered in a second column as an ethanol side stream.

FIELD OF THE INVENTION

The present invention relates generally to processes for producingalcohol and, in particular, to a process for recovering ethanol from acrude ethanol product comprising ethanol, ethyl acetate, acetic acid andwater.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from petrochemicalfeed stocks, such as oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosematerials, such as corn or sugar cane. Conventional methods forproducing ethanol from petrochemical feed stocks, as well as fromcellulose materials, include the acid-catalyzed hydration of ethylene,methanol homologation, direct alcohol synthesis, and Fischer-Tropschsynthesis. Instability in petrochemical feed stock prices contributes tofluctuations in the cost of conventionally produced ethanol, making theneed for alternative sources of ethanol production all the greater whenfeed stock prices rise. Starchy materials, as well as cellulosematerial, are converted to ethanol by fermentation. However,fermentation is typically used for consumer production of ethanol, whichis suitable for fuels or human consumption. In addition, fermentation ofstarchy or cellulose materials competes with food sources and placesrestraints on the amount of ethanol that can be produced for industrialuse.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. During the reduction of alkanoicacids, e.g., acetic acid, other compounds are formed with ethanol or areformed in side reactions. These impurities limit the production andrecovery of ethanol from such reaction mixtures. For example, duringhydrogenation, esters are produced that together with ethanol and/orwater form azeotropes, which are difficult to separate. In addition,when conversion is incomplete, acid remains in the crude ethanolproduct, which must be removed to recover ethanol.

EP02060553 describes a process for converting hydrocarbons to ethanolinvolving converting the hydrocarbons to ethanoic acid and hydrogenatingthe ethanoic acid to ethanol. The stream from the hydrogenation reactoris separated to obtain an ethanol stream and a stream of acetic acid andethyl acetate, which is recycled to the hydrogenation reactor.

The need remains for improved processes for recovering ethanol from acrude product obtained by reducing alkanoic acids, such as acetic acid,and/or other carbonyl group-containing compounds.

SUMMARY OF THE INVENTION

The present invention relates to low energy processes for recovering analcohol such as ethanol from a crude alcohol product. In one embodiment,the invention is a process for producing ethanol comprisinghydrogenating acetic acid in a reactor in the presence of a catalyst toform a crude ethanol product. At least a portion of the crude ethanolproduct is separated in a first distillation column to yield a firstdistillate comprising ethyl acetate and a first residue comprisingethanol, acetic acid and water. A majority of the ethanol in the crudeethanol product that is fed to the first column is removed in the firstresidue. At least a portion of first residue is separated in a secondcolumn to yield a side stream comprising ethanol and a second residuecomprising residual acetic acid and/or water. Preferably, the secondcolumn also forms a second distillate for separating residual ethylacetate from the first residue.

Thus, in one embodiment, the invention is to a process for producingethanol, comprising: (a) hydrogenating acetic acid in a reactor in thepresence of a catalyst to form a crude ethanol product; (b) separatingat least a portion of the crude ethanol product in a first column toyield a first distillate comprising ethyl acetate and a first residuecomprising ethanol; and (c) recovering an ethanol side stream from atleast a portion of the first residue in a second column. The secondcolumn also preferably forms a second distillate comprising at least 1wt. % ethyl acetate or at least 5 wt. % ethyl acetate, and the processoptionally further comprises the step of recycling at least a portion ofthe second distillate to the reactor. The ethanol side stream preferablycomprises at least 50 wt. % ethanol, or at least 88 wt. % ethanol. Atleast a portion of the first distillate optionally is returned to thereactor.

In another embodiment, the invention is to a process for producingethanol, comprising: (a) providing a crude ethanol product comprisingethanol and ethyl acetate (b) separating at least a portion of the crudeethanol product in a first column to yield a first distillate comprisingethyl acetate and a first residue comprising ethanol; and (c) recoveringan ethanol side stream from at least a portion of the first residue in asecond column.

In another embodiment, the invention is to a process for producingethanol, comprising hydrogenating acetic acid in a reactor in thepresence of a catalyst to form a crude ethanol product; separating aportion of the crude ethanol product in a first column to yield a firstdistillate comprising ethyl acetate and a first residue comprisingethanol, acetic acid and water, wherein a majority of the ethanol in thecrude ethanol product that is fed to the first column is removed in thefirst residue; and separating at least a portion of first residue in asecond column to yield a side stream comprising ethanol and a secondresidue comprising water and residual acetic acid. Preferably, at least70% of the ethanol in the crude ethanol product is removed in the firstresidue stream. The first residue optionally exits the firstdistillation column at a temperature from 70 to 155° C.

In another embodiment, the invention is to a process for producingethanol, comprising: (a) providing a crude ethanol product; (b)separating a portion of the crude ethanol product in a first column toyield a first distillate comprising ethyl acetate and a first residuecomprising ethanol, acetic acid and water, wherein a majority of theethanol in the crude ethanol product that is fed to the first column isremoved in the first residue; and (c) separating at least a portion offirst residue in a second column to yield a side stream comprisingethanol and a second residue comprising water and residual acetic acid.

In another embodiment, the invention is to a process for producingethanol, comprising: (a) hydrogenating acetic acid in a reactor in thepresence of a catalyst to form a crude ethanol product; (b) separating aportion of the crude ethanol product in a first column to yield a firstdistillate comprising ethyl acetate and a first residue comprisingethanol, acetic acid and water, wherein a majority of the ethanol in thecrude ethanol product that is fed to the column is removed in the firstresidue; and (c) separating at least a portion of first residue in asecond column to yield a second distillate comprising residual ethylacetate and a side stream comprising ethanol.

In another embodiment, the invention is to a process for producingethanol, comprising providing a crude ethanol product comprisingethanol, ethyl acetate, water, and acetic acid; separating a portion ofthe crude ethanol product in a first column to yield a first distillatecomprising ethyl acetate and a first residue comprising ethanol, aceticacid and water, wherein a majority of the ethanol in the crude ethanolproduct that is fed to the column is removed in the first residue; andseparating at least a portion of first residue in a second column toyield a second distillate comprising residual ethyl acetate and a sidestream comprising ethanol.

In one aspect, the process further comprises the step of hydrolyzing atleast a portion of the first distillate in a hydrolysis unit to form ahydrolysis product comprising ethanol and acetic acid, and optionallydirecting at least a portion of the hydrolysis product to the reactor.The water for the optional hydrolysis step may be derived, for example,from at least in part from the second residue.

Preferably, at least 70% of the ethanol in the crude ethanol product isremoved in the first residue stream. The resulting first residue maycomprise from 10 to 75 wt. % ethanol, from 0.01 to 35 wt. % acetic acid,and from 25 to 70 wt. % water. The first distillate optionally comprisesfrom 10 to 85 wt. % ethyl acetate, from 0.1 to 70 wt. % acetaldehyde,less than 55 wt. % ethanol, and less than 20 wt. % water.

The process optionally further comprises reducing the water content ofthe side stream to yield an ethanol product stream with reduced watercontent. Thus, in one aspect, the process further comprises separatingat least a portion of the side stream with a membrane into a permeatestream comprising water and a retentate stream comprising ethanol andless water than the at least a portion of the side stream. In analternative embodiment, the process optionally further comprisesextracting at least a portion of the side stream with one or moreextractive agents to yield an ethanol product stream with a reducedwater content. The resulting side stream may comprise 75 to 96 wt. %ethanol, less than 12 wt. % water, less than 1 wt. % acetic acid, andless than 5 wt. % ethyl acetate. Preferably, the side stream comprisesless than 1 wt. % ethyl acetate and less than 3 wt. % water.

In one aspect, the acetic acid is formed from methanol and carbonmonoxide, and each of the methanol, the carbon monoxide, and hydrogenfor the hydrogenating step is derived from syngas, and the syngas isderived from a carbon source selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawing.

FIG. 1 is a schematic diagram of an ethanol production system with twoseparation columns to recover ethanol according to one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Introduction

The present invention relates to processes for recovering ethanolproduced by hydrogenating acetic acid in the presence of a catalyst. Thehydrogenation reaction produces a crude ethanol product that comprisesethanol, water, ethyl acetate, acetic acid, and other impurities. Theprocesses of the present invention involve separating the crude ethanolproduct in a first column into a first residue stream comprisingethanol, water, and acetic acid and a distillate stream comprising ethylacetate. At least a portion of the first residue stream is separated ina second distillation column to yield a first distillate comprisingresidual ethyl acetate, an ethanol side stream and a second residuecomprising water and residual acetic acid. The ethanol side stream mayconstitute a salable ethanol composition suitable for many applications,or may be further processed, for example to remove residual water.Advantageously, this separation approach results in reducing energyrequirements to recover ethanol from the crude ethanol product.

In recovering ethanol, the processes of the present invention usecolumns, preferably distillation columns. In preferred embodiments, thefirst residue stream comprises a substantial portion of the ethanol,water, and the acetic acid from the crude ethanol product. The firstresidue stream, for example, may comprise at least 50% of the ethanolfrom the crude ethanol product, and more preferably at least 70%. Interms of ranges, the residue stream may comprise from 50% to 97.5% ofthe ethanol from the crude ethanol product, and more preferably from 70%to 99.9%. The amount of ethanol from the crude ethanol recovered in thefirst residue may be greater than 97.5%, e.g., up to 99.9%, when theethyl acetate concentration in the crude ethanol product is less than 2wt. %. In some embodiments, depending on the ethyl acetateconcentration, taking too much ethanol in the first residue may causeundesirable leakage of ethyl acetate in the residue, although the secondcolumn, discussed below, may be able to remove residual ethyl acetatethat leaks into the first residue. It is preferred that only a minoramount of ethyl acetate, if any, is withdrawn in the first residue. Insome embodiments, the first residue comprises ethyl acetate in an amountless than 1000 wppm, less than 100 wppm, less than 50 wppm. In otheraspects, the first residue may comprise greater amounts of ethyl acetatesince the second column has the ability to remove residual ethylacetate. For example, the first residue may comprise up to 0.1 wt. %ethyl acetate, up to 0.5 wt. % ethyl acetate or up to 1 wt. % ethylacetate.

In preferred embodiments, the first residue comprises a substantialportion of the water and the acetic acid from the crude ethanol product.The first residue may comprise, for example, at least 80% of the waterfrom the crude ethanol product, and more preferably at least 90%. Interms of ranges, the first residue preferably comprises from 80% to99.4% of the water from the crude ethanol product, and more preferablyfrom 90% to 99.4%. The residue stream may comprise at least 85% of theacetic acid from the crude ethanol product, e.g., at least 90% and morepreferably about 100%. In terms of ranges, the residue stream preferablycomprises from 85% to 100% of the acetic acid from the crude ethanolproduct, and more preferably from 90% to 100%. In one embodiment,substantially all of the acetic acid is recovered in the residue stream.

The first residue, which comprise ethanol, water, and acetic acid, maybe further separated to recover ethanol. In one preferred embodiment,the water and acetic acid may be removed in a second residue in a secondcolumn.

In an exemplary embodiment, the energy requirements by the initialcolumn in the process according to the present invention may be lessthan 5.5 MMBtu per ton of refined ethanol, e.g., less than 4.5 MMBtu perton of refined ethanol or less than 3.5 MMBtu per ton of refinedethanol.

The distillate from the first column may comprise light organics, suchas ethyl acetate and acetaldehyde. Removing these components from thecrude ethanol product in the first column provides an efficient meansfor removing light organics. In addition, the light organics are notcarried over with the ethanol when multiple columns are used, thusreducing the formation of byproducts that may be formed from the lightorganics. In one embodiment, the light organics are returned to thereactor, where the acetaldehyde and the ethyl acetate may be convertedto additional ethanol. Thus, all or a portion of the first distillatemay be recycled to the hydrogenation reactor. In some embodiments, thelight organics may be separated so that one stream comprising primarilyacetaldehyde and/or ethyl acetate is returned to the reactor. In anotherembodiment, the light organics may be purged from the system.

Hydrogenation of Acetic Acid

The process of the present invention may be used with any hydrogenationprocess for producing ethanol. The materials, catalysts, reactionconditions, and separation processes that may be used in thehydrogenation of acetic acid are described further below.

The raw materials, acetic acid and hydrogen, used in connection with theprocess of this invention may be derived from any suitable sourceincluding natural gas, petroleum, coal, biomass, and so forth. Asexamples, acetic acid may be produced via methanol carbonylation,acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, andanaerobic fermentation. Methanol carbonylation processes suitable forproduction of acetic acid are described in U.S. Pat. Nos. 7,208,624;7,115,772; 7,005,541; 6,657,078; 6,627,770; 6,143,930; 5,599,976;5,144,068; 5,026,908; 5,001,259; and 4,994,608, the entire disclosuresof which are incorporated herein by reference. Optionally, theproduction of ethanol may be integrated with such methanol carbonylationprocesses.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from alternate carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from other available carbonsource. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process may be derivedpartially or entirely from syngas. For example, the acetic acid may beformed from methanol and carbon monoxide, both of which may be derivedfrom syngas. The syngas may be formed by partial oxidation reforming orsteam reforming, and the carbon monoxide may be separated from syngas.Similarly, hydrogen that is used in the step of hydrogenating the aceticacid to form the crude ethanol product may be separated from syngas. Thesyngas, in turn, may be derived from variety of carbon sources. Thecarbon source, for example, may be selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.Syngas or hydrogen may also be obtained from bio-derived methane gas,such as bio-derived methane gas produced by landfills or agriculturalwaste.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteriodes, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodesamylophilus and Bacteriodes ruminicola. Optionally in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. Nos. 6,509,180;6,927,048; 7,074,603; 7,507,562; 7,351,559; 7,601,865; 7,682,812; and7,888,082, the entireties of which are incorporated herein by reference.See also US Publ. Nos. 2008/0193989 and 2009/0281354, the entireties ofwhich are incorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety ofwhich is incorporated herein by reference. Another biomass source isblack liquor, a thick, dark liquid that is a byproduct of the Kraftprocess for transforming wood into pulp, which is then dried to makepaper. Black liquor is an aqueous solution of lignin residues,hemicellulose, and inorganic chemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by converting carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into synthesis gas, andU.S. Pat. No. 6,685,754, which discloses a method for the production ofa hydrogen-containing gas composition, such as a synthesis gas includinghydrogen and carbon monoxide, are incorporated herein by reference intheir entireties.

The acetic acid fed to the hydrogenation reaction may also compriseother carboxylic acids and anhydrides, as well as acetaldehyde andacetone. Preferably, a suitable acetic acid feed stream comprises one ormore of the compounds selected from the group consisting of acetic acid,acetic anhydride, acetaldehyde, ethyl acetate, and mixtures thereof.These other compounds may also be hydrogenated in the processes of thepresent invention. In some embodiments, the presence of carboxylicacids, such as propanoic acid or its anhydride, may be beneficial inproducing propanol. Water may also be present in the acetic acid feed.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the ethanol synthesis reaction zones of thepresent invention without the need for condensing the acetic acid andlight ends or removing water, saving overall processing costs.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid may be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment, the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is mixed with other gases before vaporizing,followed by heating the mixed vapors up to the reactor inlettemperature. Preferably, the acetic acid is transferred to the vaporstate by passing hydrogen and/or recycle gas through the acetic acid ata temperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

Some embodiments of the process of hydrogenating acetic acid to formethanol may include a variety of configurations using a fixed bedreactor or a fluidized bed reactor. In many embodiments of the presentinvention, an “adiabatic” reactor can be used; that is, there is littleor no need for internal plumbing through the reaction zone to add orremove heat. In other embodiments, a radial flow reactor or reactors maybe employed, or a series of reactors may be employed with or withoutheat exchange, quenching, or introduction of additional feed material.Alternatively, a shell and tube reactor provided with a heat transfermedium may be used. In many cases, the reaction zone may be housed in asingle vessel or in a series of vessels with heat exchangerstherebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably, the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may rangefrom 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to300° C., or from 250° C. to 300° C. The pressure may range from 10 kPato 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 1500 kPa.The reactants may be fed to the reactor at a gas hourly space velocity(GHSV) of greater than 500 hr⁻¹, e.g., greater than 1000 hr⁻¹, greaterthan 2500 hr⁻¹ or even greater than 5000 hr⁻¹. In terms of ranges theGHSV may range from 50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500 hr⁻¹ to30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to 6500hr⁻¹.

The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 12:1 to 1:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature, andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,of from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to30 seconds.

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst. Suitable hydrogenationcatalysts include catalysts comprising a first metal and optionally oneor more of a second metal, a third metal or any number of additionalmetals, optionally on a catalyst support. The first and optional secondand third metals may be selected from Group IB, IIB, IIIB, IVB, VB,VIIB, VIIB, VIII transition metals, a lanthanide metal, an actinidemetal or a metal selected from any of Groups IIIA, IVA, VA, and VIA.Preferred metal combinations for some exemplary catalyst compositionsinclude platinum/tin, platinum/ruthenium, platinum/rhenium,palladium/ruthenium, palladium/rhenium, cobalt/palladium,cobalt/platinum, cobalt/chromium, cobalt/ruthenium, cobalt/tin,silver/palladium, copper/palladium, copper/zinc, nickel/palladium,gold/palladium, ruthenium/rhenium, and ruthenium/iron. Exemplarycatalysts are further described in U.S. Pat. No. 7,608,744 and U.S. Pub.No. 2010/0029995, the entireties of which are incorporated herein byreference. In another embodiment, the catalyst comprises a Co/Mo/Scatalyst of the type described in U.S. Pub. No. 2009/0069609, theentirety of which is incorporated herein by reference.

In one embodiment, the catalyst comprises a first metal selected fromthe group consisting of copper, iron, cobalt, nickel, ruthenium,rhodium, palladium, osmium, iridium, platinum, titanium, zinc, chromium,rhenium, molybdenum, and tungsten. Preferably, the first metal isselected from the group consisting of platinum, palladium, cobalt,nickel, and ruthenium. More preferably, the first metal is selected fromplatinum and palladium. In embodiments of the invention where the firstmetal comprises platinum, it is preferred that the catalyst comprisesplatinum in an amount less than 5 wt. %, e.g., less than 3 wt. % or lessthan 1 wt. %, due to the high commercial demand for platinum.

As indicated above, in some embodiments, the catalyst further comprisesa second metal, which typically would function as a promoter. Ifpresent, the second metal preferably is selected from the groupconsisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. More preferably, the second metal is selectedfrom the group consisting of copper, tin, cobalt, rhenium, and nickel.More preferably, the second metal is selected from tin and rhenium.

In certain embodiments where the catalyst includes two or more metals,e.g., a first metal and a second metal, the first metal is present inthe catalyst in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt.%, or from 0.1 to 3 wt. %. The second metal preferably is present in anamount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to5 wt. %. For catalysts comprising two or more metals, the two or moremetals may be alloyed with one another or may comprise a non-alloyedmetal solution or mixture.

The preferred metal ratios may vary depending on the metals used in thecatalyst. In some exemplary embodiments, the mole ratio of the firstmetal to the second metal is from 10:1 to 1:10, e.g., from 4:1 to 1:4,from 2:1 to 1:2, from 1.5:1 to 1:1.5 or from 1.1:1 to 1:1.1.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin,and rhenium. More preferably, the third metal is selected from cobalt,palladium, and ruthenium. When present, the total weight of the thirdmetal preferably is from 0.05 to 4 wt. %, e.g., from 0.1 to 3 wt. %, orfrom 0.1 to 2 wt. %.

In addition to one or more metals, in some embodiments of the presentinvention the catalysts further comprise a support or a modifiedsupport. As used herein, the term “modified support” refers to a supportthat includes a support material and a support modifier, which adjuststhe acidity of the support material.

The total weight of the support or modified support, based on the totalweight of the catalyst, preferably is from 75 to 99.9 wt. %, e.g., from78 to 97 wt. %, or from 80 to 95 wt. %. In preferred embodiments thatutilize a modified support, the support modifier is present in an amountfrom 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %, from 0.5 to 15 wt. %,or from 1 to 8 wt. %, based on the total weight of the catalyst. Themetals of the catalysts may be dispersed throughout the support, layeredthroughout the support, coated on the outer surface of the support(i.e., egg shell), or decorated on the surface of the support.

As will be appreciated by those of ordinary skill in the art, supportmaterials are selected such that the catalyst system is suitably active,selective and robust under the process conditions employed for theformation of ethanol.

Suitable support materials may include, for example, stable metaloxide-based supports or ceramic-based supports. Preferred supportsinclude silicaceous supports, such as silica, silica/alumina, a GroupIIA silicate such as calcium metasilicate, pyrogenic silica, high puritysilica, and mixtures thereof. Other supports may include, but are notlimited to, iron oxide, alumina, titania, zirconia, magnesium oxide,carbon, graphite, high surface area graphitized carbon, activatedcarbons, and mixtures thereof.

As indicated, the catalyst support may be modified with a supportmodifier. In some embodiments, the support modifier may be an acidicmodifier that increases the acidity of the catalyst. Suitable acidicsupport modifiers may be selected from the group consisting of: oxidesof Group IVB metals, oxides of Group VB metals, oxides of Group VIBmetals, oxides of Group VIIB metals, oxides of Group VIIIB metals,aluminum oxides, and mixtures thereof. Acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,Al₂O₃, B₂O₃, P₂O₅, and Sb₂O₃. Preferred acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,and Al₂O₃. The acidic modifier may also include WO₃, MoO₃, Fe₂O₃, Cr₂O₃,V₂O₅, MnO₂, CuO, Co₂O₃, and Bi₂O₃.

In another embodiment, the support modifier may be a basic modifier thathas a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group 111B metaloxides, (viii) Group 111B metal metasilicates, and mixtures thereof. Inaddition to oxides and metasilicates, other types of modifiers includingnitrates, nitrites, acetates, and lactates may be used. Preferably, thesupport modifier is selected from the group consisting of oxides andmetasilicates of any of sodium, potassium, magnesium, calcium, scandium,yttrium, and zinc, as well as mixtures of any of the foregoing. Morepreferably, the basic support modifier is a calcium silicate, and evenmore preferably calcium metasilicate (CaSiO₃). If the basic supportmodifier comprises calcium metasilicate, it is preferred that at least aportion of the calcium metasilicate is in crystalline form.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint Gobain Nor Pro. The Saint-Gobain NorPro SS61138 silica exhibits the following properties: containsapproximately 95 wt. % high surface area silica; surface area of about250 m²/g; median pore diameter of about 12 nm; average pore volume ofabout 1.0 cm³/g as measured by mercury intrusion porosimetry and apacking density of about 0.352 g/cm³ (22 lb/ft³).

A preferred silica/alumina support material is KA-160 silica spheresfrom Sud Chemie having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, an absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. Nos. 7,608,744 and 7,863,489 and U.S. Pub. No. 2010/0197485referred to above, the entireties of which are incorporated herein byreference.

In particular, the hydrogenation of acetic acid may achieve favorableconversion of acetic acid and favorable selectivity and productivity toethanol. For purposes of the present invention, the term “conversion”refers to the amount of acetic acid in the feed that is converted to acompound other than acetic acid. Conversion is expressed as a molepercentage based on acetic acid in the feed. The conversion may be atleast 10%, e.g., at least 20%, at least 40%, at least 50%, at least 60%,at least 70% or at least 80%. Although catalysts that have highconversions are desirable, such as at least 80% or at least 90%, in someembodiments a low conversion may be acceptable at high selectivity forethanol. It is, of course, well understood that in many cases, it ispossible to compensate for conversion by appropriate recycle streams oruse of larger reactors, but it is more difficult to compensate for poorselectivity.

Selectivity is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 60 mole % of the converted acetic acidis converted to ethanol, we refer to the ethanol selectivity as 60%.Preferably, the catalyst selectivity to ethoxylates is at least 60%,e.g., at least 70%, or at least 80%. As used herein, the term“ethoxylates” refers specifically to the compounds ethanol,acetaldehyde, and ethyl acetate. Preferably, the selectivity to ethanolis at least 80%, e.g., at least 85% or at least 88%. Preferredembodiments of the hydrogenation process also have low selectivity toundesirable products, such as methane, ethane, and carbon dioxide. Theselectivity to these undesirable products preferably is less than 4%,e.g., less than 2% or less than 1%. More preferably, these undesirableproducts are present in undetectable amounts. Formation of alkanes maybe low, and ideally less than 2%, less than 1%, or less than 0.5% of theacetic acid passed over the catalyst is converted to alkanes, which havelittle value other than as fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. A productivity of at least100 grams of ethanol per kilogram of catalyst per hour, e.g., at least400 grams of ethanol per kilogram of catalyst per hour or at least 600grams of ethanol per kilogram of catalyst per hour, is preferred. Interms of ranges, the productivity preferably is from 100 to 3,000 gramsof ethanol per kilogram of catalyst per hour, e.g., from 400 to 2,500grams of ethanol per kilogram of catalyst per hour or from 600 to 2,000grams of ethanol per kilogram of catalyst per hour.

Operating under the conditions of the present invention may result inethanol production on the order of at least 0.1 tons of ethanol perhour, e.g., at least 1 ton of ethanol per hour, at least 5 tons ofethanol per hour, or at least 10 tons of ethanol per hour. Larger scaleindustrial production of ethanol, depending on the scale, generallyshould be at least 1 ton of ethanol per hour, e.g., at least 15 tons ofethanol per hour or at least 30 tons of ethanol per hour. In terms ofranges, for large scale industrial production of ethanol, the process ofthe present invention may produce from 0.1 to 160 tons of ethanol perhour, e.g., from 15 to 160 tons of ethanol per hour or from 30 to 80tons of ethanol per hour. Ethanol production from fermentation, due theeconomies of scale, typically does not permit the single facilityethanol production that may be achievable by employing embodiments ofthe present invention.

In various embodiments of the present invention, the crude ethanolproduct produced by the hydrogenation process, before any subsequentprocessing, such as purification and separation, will typically compriseacetic acid, ethanol and water. As used herein, the term “crude ethanolproduct” refers to any composition comprising from 5 to 70 wt. % ethanoland from 5 to 40 wt. % water. Exemplary compositional ranges for thecrude ethanol product are provided in Table 1. The “others” identifiedin Table 1 may include, for example, esters, ethers, aldehydes, ketones,alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 70 15 to 70  15to 50 25 to 50 Acetic Acid 0 to 90 0 to 50 15 to 70 20 to 70 Water 5 to40 5 to 30 10 to 30 10 to 26 Ethyl Acetate 0 to 30 0 to 20  1 to 12  3to 10 Acetaldehyde 0 to 10 0 to 3  0.1 to 3  0.2 to 2  Others 0.1 to 10 0.1 to 6   0.1 to 4  —

In one embodiment, the crude ethanol product comprises acetic acid in anamount less than 20 wt. %, e.g., less than 15 wt. %, less than 10 wt. %or less than 5 wt. %. In embodiments having lower amounts of aceticacid, the conversion of acetic acid is preferably greater than 75%,e.g., greater than 85% or greater than 90%. In addition, the selectivityto ethanol may also be preferably high, and is preferably greater than75%, e.g., greater than 85% or greater than 90%.

Ethanol Recovery

An exemplary ethanol recovery system according to one embodiment of thepresent invention is shown in FIG. 1. Hydrogenation system 100 providesa suitable hydrogenation reactor and a process for separating ethanolfrom the crude reaction mixture according to an embodiment of theinvention. System 100 comprises reaction zone 101 and separation zone102. Reaction zone 101 comprises reactor 103, hydrogen feed line 104 andacetic acid feed line 105. Separation zone 102 comprises a separator106, e.g., a flash vessel, and distillation columns.

Hydrogen and an akanoic acid, preferably acetic acid, are fed to avaporizer 109 via lines 104 and 105, respectively, to create a vaporfeed stream in line 110 that is directed to reactor 103. In oneembodiment, lines 104 and 105 may be combined and jointly fed to thevaporizer 109. The temperature of the vapor feed stream in line 110 ispreferably from 100° C. to 350° C., e.g., from 120° C. to 310° C. orfrom 150° C. to 300° C. Any feed that is not vaporized is removed fromvaporizer 109, and may be recycled or discarded. In addition, althoughline 110 is shown as being directed to the top of reactor 103, line 110may be directed to the side, upper portion, or bottom of reactor 103.Further modifications and additional components to reaction zone 101 andseparation zone 102 are described below.

Reactor 103 contains the catalyst that is used in the hydrogenation ofthe alkanoic acid, preferably acetic acid. In one embodiment, one ormore guard beds (not shown) may be used upstream of the reactor,optionally upstream of vaporizer 109, to protect the catalyst frompoisons or undesirable impurities contained in the feed orreturn/recycle streams. Such guard beds may be employed in the vapor orliquid streams. Suitable guard bed materials may include, for example,carbon, silica, alumina, ceramic, or resins. In one aspect, the guardbed media is functionalized, e.g., silver functionalized, to trapparticular species such as sulfur or halogens. During the hydrogenationprocess, a crude ethanol product stream is withdrawn, preferablycontinuously, from reactor 103 via line 111.

The crude ethanol product stream may be condensed and fed to a separator106, which, in turn, forms a vapor stream 112 and a liquid stream 113.In some embodiments, separator 106 may comprise a flasher or a knockoutpot. The separator 106 may operate at a temperature of from 20° C. to250° C., e.g., from 30° C. to 225° C. or from 60° C. to 200° C. Thepressure of separator 106 may be from 50 kPa to 2000 kPa, e.g., from 75kPa to 1500 kPa or from 100 kPa to 1000 kPa. Optionally, the crudeethanol product in line 111 may pass through one or more membranes toseparate hydrogen and/or other non-condensable gases.

The vapor stream 112 exiting separator 106 may comprise hydrogen andhydrocarbons, and may be purged and/or returned to reaction zone 101. Asshown, vapor stream 112 is combined with the hydrogen feed 104 andco-fed to vaporizer 109. In some embodiments, the returned vapor stream112 may be compressed before being combined with hydrogen feed 104.

The liquid stream 113 from separator 106 is withdrawn and directed as afeed composition to the side of first distillation column 107, alsoreferred to as a “light ends column.” In one embodiment, the contents ofliquid stream 113 are substantially similar to the crude ethanol productobtained from the reactor, except that the composition has been depletedof hydrogen, carbon dioxide, methane or ethane, which have been removedby separator 106. Accordingly, liquid stream 113 may also be referred toas a crude ethanol product. Exemplary components of liquid stream 113are provided in Table 2. It should be understood that liquid stream 113may contain other components, not listed in Table 2, such as componentsderived from the feed.

TABLE 2 COLUMN FEED COMPOSITION (Liquid Stream 113) Conc. Conc. Conc.(wt. %) (wt. %) (wt. %) Ethanol 5 to 70    10 to 60 15 to 50 Acetic Acid<90    5 to 80 15 to 70 Water 5 to 45    5 to 30 10 to 30 Ethyl Acetate<35  0.001 to 15  1 to 12 Acetaldehyde <10 0.001 to 3 0.1 to 3  Acetal<5 0.001 to 2 0.005 to 1    Acetone <5  0.0005 to 0.05 0.001 to 0.03 Other Esters <5 <0.005 <0.001 Other Ethers <5 <0.005 <0.001 OtherAlcohols <5 <0.005 <0.001

The amounts indicated as less than (<) in the tables throughout thepresent specification are preferably not present and if present may bepresent in trace amounts or in amounts greater than 0.0001 wt. %.

The “other esters” in Table 2 may include, but are not limited to, ethylpropionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butylacetate or mixtures thereof. The “other ethers” in Table 2 may include,but are not limited to, diethyl ether, methyl ethyl ether, isobutylethyl ether or mixtures thereof. The “other alcohols” in Table 2 mayinclude, but are not limited to, methanol, isopropanol, n-propanol,n-butanol or mixtures thereof. In one embodiment, liquid stream 113 maycomprise propanol, e.g., isopropanol and/or n-propanol, in an amountfrom 0.001 to 0.1 wt. %, from 0.001 to 0.05 wt. % or from 0.001 to 0.03wt. %. In should be understood that these other components may becarried through in any of the distillate or residue streams describedherein and will not be further described herein, unless indicatedotherwise.

Optionally, crude ethanol product in line 111 or in liquid stream 113may be further fed to an esterification reactor, hydrogenolysis reactor,or combination thereof. An esterification reactor may be used to consumeacetic acid present in the crude ethanol product to further reduce theamount of acetic acid to be removed. Hydrogenolysis may be used toconvert ethyl acetate in the crude ethanol product to ethanol.

In the embodiment shown in FIG. 1, liquid stream 113 is introduced inthe upper part of first column 107, e.g., upper half or upper third. Inone embodiment, no entrainers are added to first column 107. In firstcolumn 107, a weight majority of the ethanol, water, acetic acid, andother heavy components, if present, are removed from liquid stream 113and are withdrawn, preferably continuously, as residue in line 114.First column 107 also forms an overhead distillate, which is withdrawnin line 115, and which may be condensed and refluxed, for example, at aratio of from 30:1 to 1:30, e.g., from 10:1 to 1:10 or from 1:5 to 5:1.The overhead distillate in stream 115 preferably comprises a weightmajority of the ethyl acetate and acetaldehyde from liquid stream 113.Beneficially, a small amount, e.g., at least 0.1 wppm, at least 1 wppm,at least 10 wppm, at least 100 wppm or at least 1000 wppm, of ethylacetate and/or acetaldehyde, separately or collectively, may bepermitted to pass into the first residue since the second column,discussed below, provides a means for effectively removing residualamounts of these compounds from the product alcohol composition.

When column 107 is operated under about 170 kPa, the temperature of theresidue exiting in line 114 preferably is from 70° C. to 155° C., e.g.,from 90° C. to 130° C. or from 100° C. to 110° C. The base of column 107may be maintained at a relatively low temperature by withdrawing aresidue stream comprising ethanol, water, and acetic acid, therebyproviding an energy efficiency advantage. The temperature of thedistillate exiting in line 115 from column 107 preferably at 170 kPa isfrom 75° C. to 100° C., e.g., from 75° C. to 83° C. or from 81° C. to84° C. In some embodiments, the pressure of first column 107 may rangefrom 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to375 kPa. Exemplary components of the distillate and residue compositionsfor first column 107 are provided in Table 3 below. It should also beunderstood that the distillate and residue may also contain othercomponents, not listed in Table 3. For convenience, the distillate andresidue of the first column may also be referred to as the “firstdistillate” or “first residue.” The distillates or residues of the othercolumns may also be referred to with similar numeric modifiers (second,third, etc.) in order to distinguish them from one another, but suchmodifiers should not be construed as requiring any particular separationorder.

TABLE 3 FIRST COLUMN 107 Conc. Conc. Conc. (wt. %) (wt. %) (wt. %)Distillate Ethyl Acetate 10 to 85 15 to 80 20 to 75 Acetaldehyde 0.1 to70  0.2 to 65  0.5 to 65  Acetal  <0.1 <0.1 <0.05 Acetone   <0.05 0.001to 0.03   0.01 to 0.025 Ethanol  3 to 55  4 to 50  5 to 45 Water 0.1 to20   1 to 15  2 to 10 Acetic Acid <2 <0.1 <0.05 Residue Acetic Acid 0.01to 35  0.1 to 30  0.2 to 25  Water 25 to 70 30 to 65 35 to 60 Ethanol 10to 75 15 to 70 20 to 65 Ethyl Acetate <1 <0.5 <0.1 

In an embodiment of the present invention, column 107 may be operated ata temperature where most of the water, ethanol, and acetic acid areremoved from the residue stream and only a small amount of ethanol andwater is collected in the distillate stream due to the formation ofbinary and tertiary azeotropes. The weight ratio of water in the residuein line 114 to water in the distillate in line 115 may be greater than1:1, e.g., greater than 2:1. The weight ratio of ethanol in the residueto ethanol in the distillate may be greater than 1:1, e.g., greater than2:1. The weight ratio of ethyl acetate in the first distillate in line115 to ethyl acetate in the first residue in line 114 may be greaterthan 1:1, e.g., greater than 2:1. The weight ratio of acetaldehyde inthe first distillate in line 115 to acetaldehyde in the first residue inline 114 may be greater than 1:1, e.g., greater than 2:1.

The amount of acetic acid in the first residue 114 may vary dependingprimarily on the conversion in reactor 103. In one embodiment, when theconversion is high, e.g., greater than 90%, the amount of acetic acid inthe first residue may be less than 10 wt. %, e.g., less than 5 wt. % orless than 2 wt. %. In other embodiments, when the conversion is lower,e.g., less than 90%, the amount of acetic acid in the first residue maybe greater than 10 wt. %.

The separation in first column 107 may be conducted with or without theaddition of an azeotrope or extractive agent.

The first distillate preferably is substantially free of acetic acid,e.g., comprising less than 1000 ppm, less than 500 ppm or less than 100ppm acetic acid. The distillate may be purged from the system orrecycled in whole or part to reactor 103. In some embodiments, thedistillate may be further separated, e.g., in a distillation column (notshown), into an acetaldehyde stream and an ethyl acetate stream. Eitherof these streams may be returned to the reactor 103 or separated fromsystem 100 as a separate product.

In one embodiment, not shown, all or a portion of the first distillateis directed to a hydrolysis unit in which the ethyl acetate containedtherein is reacted with water to form ethanol and acetic acid, both ofwhich may be recycled to the reactor or sent to the separation systemfor recovery. Thus, in one embodiment, the process includes the step ofhydrolyzing at least a portion of the first distillate in a hydrolysisunit to form a hydrolysis product comprising ethanol and acetic acid anddirecting at least a portion of the hydrolysis product to the reactor orseparation system, e.g., to the first column or the second column. Inanother aspect, all or a portion of the first distillate is recycled tothe reactor without hydrolysis.

Some species, such as acetals, may decompose in first column 107 suchthat very low amounts, or even no detectable amounts, of acetals remainin the distillate or residue.

In addition, an equilibrium reaction between acetic acid/ethanol andethyl acetate may occur in the crude ethanol product after it exitsreactor 103. Depending on the concentration of acetic acid in the crudeethanol product, this equilibrium may be driven toward formation ofethyl acetate. This reaction may be regulated through the residence timeand/or temperature of the crude ethanol product.

The columns shown in FIG. 1 may comprise any distillation column capableof performing the desired separation and/or purification. Each columnpreferably comprises a tray column having from 1 to 150 trays, e.g.,from 10 to 100 trays, from 20 to 95 trays or from 30 to 75 trays. Thetrays may be sieve trays, fixed valve trays, movable valve trays, or anyother suitable design known in the art. In other embodiments, a packedcolumn may be used. For packed columns, structured packing or randompacking may be employed. The trays or packing may be arranged in onecontinuous column or they may be arranged in two or more columns suchthat the vapor from the first section enters the second section whilethe liquid from the second section enters the first section, etc.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in the figures. Heat may besupplied to the base of each column or to a circulating bottom streamthrough a heat exchanger or reboiler. Other types of reboilers, such asinternal reboilers, may also be used. The heat that is provided to thereboilers may be derived from any heat generated during the process thatis integrated with the reboilers or from an external source such asanother heat generating chemical process or a boiler. Although onereactor and one flasher are shown in the figures, additional reactors,flashers, condensers, heating elements, and other components may be usedin various embodiments of the present invention. As will be recognizedby those skilled in the art, various condensers, pumps, compressors,reboilers, drums, valves, connectors, separation vessels, etc., normallyemployed in carrying out chemical processes may also be combined andemployed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary. As apractical matter, pressures from 10 kPa to 3000 kPa will generally beemployed in these zones although in some embodiments subatmosphericpressures or superatmospheric pressures may be employed. Temperatureswithin the various zones will normally range between the boiling pointsof the composition removed as the distillate and the composition removedas the residue. As will be recognized by those skilled in the art, thetemperature at a given location in an operating distillation column isdependent on the composition of the material at that location and thepressure of column. In addition, feed rates may vary depending on thesize of the production process and, if described, may be genericallyreferred to in terms of feed weight ratios.

To recover ethanol, the residue in line 114 may be further separateddepending on the concentration of acetic acid, water and/or ethylacetate. In most embodiments of the present invention, residue in line114 is further separated in a second column 119. In FIG. 1, the secondcolumn 119 is referred to as an “acid separation column,” because thesecond residue 122 comprises acetic acid and water. An acid separationcolumn may be used, for example, when the acetic acid concentration inthe first residue is greater than 1 wt. %, e.g., greater than 5 wt. %.

In FIG. 1, the first residue in line 114 is introduced to second column119, e.g., acid separation column, preferably in the top part of column108, e.g., top half or top third. Second column 119 yields a secondresidue in line 122 comprising acetic acid and water, a seconddistillate in line 120 comprising residual ethyl acetate and/or residualacetaldehyde, and an ethanol side stream 121 comprising ethanol. Byyielding product ethanol in a side stream, while separating water,acetic acid and residual ethyl acetate, the present invention provides alow energy solution, optionally having only two columns, for recoveringethanol from a crude ethanol product. Second column 108 may be a traycolumn or packed column. In one embodiment, second column 108 is a traycolumn having from 5 to 150 trays, e.g., from 15 to 50 trays or from 20to 45 trays. Although the temperature and pressure of second column 119may vary, when at atmospheric pressure the temperature of the secondresidue exiting in line 122 from second column 119 preferably is from95° C. to 130° C., e.g., from 100° C. to 125° C. or from 110° C. to 120°C. The temperature of the second distillate exiting in line 120 fromsecond column 119 preferably is from 60° C. to 105° C., e.g., from 75°C. to 100° C. or from 80° C. to 100° C. The temperature of the ethanolside stream exiting in line 121 preferably is from 60° C. to 105° C.,e.g., from 75° C. to 100° C. or from 80° C. to 100° C. The pressure ofsecond column 119 may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to475 kPa or from 1 kPa to 375 kPa. Exemplary components for thedistillate and residue compositions for second column 119 are providedin Table 4 below. It should be understood that the distillate andresidue may also contain other components, not listed in Table 4, suchas components derived from the feed.

TABLE 4 SECOND COLUMN 119 Conc. Conc. Conc. (wt. %) (wt. %) (wt. %)Second Distillate Ethyl Acetate  5 to 90 10 to 80  15 to 75 Acetaldehyde<60  1 to 40   1 to 35 Ethanol <45 0.001 to 40   0.01 to 35 Water <200.01 to 10  0.1 to 5 Side Stream Ethanol 50 to 99 60 to 99  70 to 99Water <15 0.01 to 10  0.1 to 8 Ethyl Acetate 0.01 to 1   0.05 to 0.75 0.1 to 0.5 Acetic Acid   <0.5 <0.01  0.001 to 0.01 Second ResidueEthanol 50 to 99 60 to 90  65 to 85 Water <20 0.001 to 15   0.01 to 10Ethyl Acetate  <1 0.001 to 2    0.001 to 0.5  Acetic Acid <15 <10    0.1to 5

The ratio of ethanol in the side stream in line 121 to ethanol in thesecond residue in line 122 preferably is at least 2:1, at least 10:1 orat least 35:1. In one embodiment, the ratio of water in the secondresidue 122 to water in the second distillate 120 is greater than 2:1,e.g., greater than 4:1 or greater than 6:1. In addition, the ratio ofacetic acid in the second residue 122 to acetic acid in the seconddistillate 120 preferably is greater than 10:1, e.g., greater than 15:1or greater than 20:1. Preferably, the second distillate in line 120 andthe side stream 121 are substantially free of acetic acid and may onlycontain, if any, trace amounts of acetic acid. A reduced concentrationof acetic acid in lines 120, 121 advantageously provides an ethanolproduct that also has no amount or a trace amount of acetic acid. Inaddition, as discussed above, an advantage of the present separationscheme is the ability to effectively remove ethyl acetate from productethanol in a two column system. In one embodiment, the ratio of ethylacetate in the second distillate in line 120 to ethyl acetate in theside stream in line 121 is greater than 2:1, greater than 5:1 or greaterthan 10:1.

The second distillate in line 118 may be purged from system or recycledin whole or part to reactor 103, along with first distillate in line115.

The second residue in line 122 comprises acetic acid and water.Depending on the amount of water and acetic acid contained in the secondresidue, the residue may be treated in one or more of the followingprocesses. The following are exemplary processes for further treatingthe residue and it should be understood that any (or none) of thefollowing may be used regardless of acid concentration. When the residuecomprises in large part acetic acid, e.g., greater than 70 wt. %, theresidue may be recycled to the reactor without any separation of thewater. In one embodiment, the residue may be separated into an aceticacid stream and a water stream when the residue comprises a majority ofacetic acid, e.g., greater than 50 wt. %. Acetic acid may also berecovered in some embodiments from the residue having a lower acidconcentration. The residue may be separated into the acetic acid andwater streams by a distillation column or one or more membranes. If amembrane or an array of membranes is employed to separate the aceticacid from the water, the membrane or array of membranes may be selectedfrom any suitable acid resistant membrane that is capable of removing apermeate water stream. The resulting acetic acid stream comprisingacetic acid optionally is returned to the reaction zone. The resultingwater stream may be used as an extractive agent or to hydrolyze anester-containing stream in a hydrolysis unit, e.g., to hydrolyze all ora portion of first distillate 115, as discussed above.

In other embodiments, for example, where the second residue comprisesless than 50 wt. % acid, possible options include one or more of: (i)returning a portion of the residue to reactor 103, (ii) neutralizing theacid, (iii) reacting the acid with an alcohol, or (iv) disposing of theresidue in a waste water treatment facility. It also may be possible toseparate a residue comprising less than 50 wt. % acetic acid using aweak acid recovery distillation column to which a solvent (optionallyacting as an azeotroping agent) may be added. Exemplary solvents thatmay be suitable for this purpose include ethyl acetate, propyl acetate,isopropyl acetate, butyl acetate, vinyl acetate, diisopropyl ether,carbon disulfide, tetrahydrofuran, isopropanol, ethanol, and C₃-C₁₂alkanes. When neutralizing the acid, it is preferred that the residuecomprises less than 10 wt. % acetic acid. The acetic acid may beneutralized with any suitable alkali or alkaline earth metal base, suchas sodium hydroxide or potassium hydroxide. When reacting acetic acidwith an alcohol, it is preferred that the residue comprises less than 50wt. % acid. The alcohol may be any suitable alcohol, such as methanol,ethanol, propanol, butanol, or mixtures thereof. The reaction forms anester that may be integrated with other systems, such as carbonylationproduction or an ester production process. Preferably, the alcoholcomprises ethanol and the resulting ester comprises ethyl acetate.Optionally, the resulting ester may be fed to the hydrogenation reactor.

In some embodiments, when the second residue comprises very minoramounts of acetic acid, e.g., less than 5 wt. %, the second residue maybe disposed of to a waste water treatment facility without furtherprocessing. The organic content, e.g., acetic acid content, of theresidue beneficially may be suitable to feed microorganisms used in awaste water treatment facility.

Depending on the water concentration, the ethanol product may be derivedfrom the side stream in line 121. In one aspect, the side stream in line121 comprises at least 88 wt. % ethanol, at least 90 wt. % ethanol, atleast 95 wt. % ethanol or at least 97 wt. % ethanol. In one embodiment,the side stream in line 121 may comprise from 75 to 96 wt. % ethanol andless than 12 wt. % water. Some applications, such as industrial ethanolapplications, may tolerate water in the ethanol product, while otherapplications, such as fuel applications, may require an anhydrousethanol. The amount of water in the side stream of line 121 may becloser to the azeotropic amount of water, e.g., at least 4 wt. %,preferably less than 20 wt. %, e.g., less than 12 wt. % or less than 7.5wt. %. Water optionally may be removed from the side stream in line 121using several different separation techniques. Residual water removalmay be accomplished, for example, using one or more adsorption units,membranes, molecular sieves, extractive distillation units, or acombination thereof. Suitable adsorption units include pressure swingadsorption systems and thermal swing adsorption units. Particularlypreferred techniques include the use of distillation column, membranes,adsorption units and combinations thereof. For example, the side streamfrom the second column may be distilled in an additional distillationcolumn to form an additional distillate comprising ethanol and anadditional residue comprising water.

As shown in FIG. 1, an adsorption unit 123 may be provided to removewater in water stream 125 from the side stream in line 121 thusproducing an anhydrous ethanol stream 124, preferably comprising 97 wt.% or more ethanol, e.g., at least 98 wt. % ethanol or at least 99.5 wt.% ethanol. The adsorption unit 123 may employ a suitable adsorptionagent such as a zeolite. In one preferred embodiment, adsorption unit123 is a pressure swing adsorption (PSA) unit that is operated at atemperature from 30° C. to 160° C., e.g., from 80° C. to 140° C., and apressure of from 0.01 kPa to 550 kPa, e.g., from 1 to 150 kPa. The PSAunit may comprise two to five beds. Adsorption unit 123 may remove atleast 95% of the water from the side stream in line 121, and morepreferably from 95% to 99.9% of the water from the side stream in line121. Water stream 125 may be combined with any other water stream fromsystem 100 and may be removed from the system or used elsewhere in thesystem, for example, as a hydrolyzing agent for the hydrolysis of ethylacetate in the first distillate. The water stream may also compriseethanol, in which case it may be desirable to feed all or a portion ofthe water stream back to first column 107 or other separation device forfurther ethanol recovery.

The ethanol product produced by the process of the present invention maybe an industrial grade ethanol comprising from 75 to 96 wt. % ethanol,e.g., from 80 to 96 wt. % or from 85 to 96 wt. % ethanol, based on thetotal weight of the ethanol product. Exemplary finished ethanolcompositional ranges are provided below in Table 5.

TABLE 5 FINISHED ETHANOL COMPOSITIONS Conc. Conc. Conc. Component (wt.%) (wt. %) (wt. %) Ethanol 75 to 96 80 to 96 85 to 96 Water <12 1 to 9 3to 8 Acetic Acid <1 <0.1 <0.01 Ethyl Acetate <2 <0.5 <0.05 Acetal <0.05<0.01 <0.005 Acetone <0.05 <0.01 <0.005 Isopropanol <0.5 <0.1 <0.05n-propanol <0.5 <0.1 <0.05

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment,the finished ethanol composition is substantially free of acetaldehyde,optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5wppm or less than 1 wppm.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingapplications as fuels, solvents, chemical feedstocks, pharmaceuticalproducts, cleansers, sanitizers, hydrogenation transport or consumption.In fuel applications, the finished ethanol composition may be blendedwith gasoline for motor vehicles such as automobiles, boats and smallpiston engine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, aldehydes, and higheralcohols, especially butanol. In the production of ethyl acetate, thefinished ethanol composition may be esterified with acetic acid. Inanother application, the finished ethanol composition may be dehydratedto produce ethylene. Any known dehydration catalyst can be employed todehydrate ethanol, such as those described in copending U.S. Pub. Nos.2010/0030002 and 2010/0030001, the entireties of which are incorporatedherein by reference. A zeolite catalyst, for example, may be employed asthe dehydration catalyst. Preferably, the zeolite has a pore diameter ofat least about 0.6 nm, and preferred zeolites include dehydrationcatalysts selected from the group consisting of mordenites, ZSM-5, azeolite X and a zeolite Y. Zeolite X is described, for example, in U.S.Pat. No. 2,882,244 and zeolite Yin U.S. Pat. No. 3,130,007, theentireties of which are hereby incorporated herein by reference.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In addition, it should be understood that aspectsof the invention and portions of various embodiments and variousfeatures recited herein and/or in the appended claims may be combined orinterchanged either in whole or in part. In the foregoing descriptionsof the various embodiments, those embodiments which refer to anotherembodiment may be appropriately combined with one or more otherembodiments, as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing ethanol, comprising: (a)hydrogenating acetic acid in a reactor in the presence of a catalyst toform a crude ethanol product; (b) separating at least a portion of thecrude ethanol product in a first column to yield a first distillatecomprising ethyl acetate and a first residue comprising ethanol; (c)hydrolyzing at least a portion of the first distillate in a hydrolysisunit to form a hydrolysis product comprising ethanol and acetic acid;(d) recovering an ethanol side stream from at least a portion of thefirst residue in a second column, wherein the ethanol side streamcomprises 75 to 96 wt. % ethanol, less than 12 wt. % water, less than 1wt. % acetic acid, and less than 5 wt. % ethyl acetate; and (e) reducingthe water content of the ethanol side stream to yield an ethanol productstream with reduced water content.
 2. The process of claim 1, whereinthe ethanol side stream comprises at least 88 wt. % ethanol.
 3. Theprocess of claim 1, wherein the second column also forms a seconddistillate comprising at least 1 wt. % ethyl acetate.
 4. The process ofclaim 1, wherein the second column also forms a second distillatecomprising at least 5 wt. % ethyl acetate.
 5. The process of claim 1,wherein the second column also forms a second distillate comprising atleast 5 wt. % ethyl acetate, the process further comprising recycling atleast a portion of the second distillate to the reactor.
 6. The processof claim 1, further comprising directing at least a portion of thehydrolysis product to the reactor.
 7. The process of claim 1, whereinthe second column also forms a second residue comprising water andacetic acid.
 8. The process of claim 1, wherein the second column alsoforms a second distillate comprising at least 1 wt. % ethyl acetate anda second residue comprising water and acetic acid.
 9. The process ofclaim 1, wherein at least 70% of the ethanol in the crude ethanolproduct is removed in the first residue stream.
 10. The process of claim1, wherein the first residue comprises 10 to 75 wt. % ethanol, 0.01 to35 wt. % acetic acid, and 25 to 70 wt. % water.
 11. The process of claim1, wherein the first distillate comprises 10 to 85 wt. % ethyl acetate,0.1 to 70 wt. % acetaldehyde, less than 55 wt. % ethanol, and less than20 wt. % water.
 12. The process of claim 1, wherein the side streamcomprises less than 1 wt. % ethyl acetate.
 13. The process of claim 1,wherein the side stream comprises less than 3 wt. % water.
 14. Theprocess of claim 1, wherein step (e) further comprises separating atleast a portion of the side stream with a membrane into a permeatestream comprising water and a retentate stream comprising ethanol andless water than the at least a portion of the side stream.
 15. Theprocess of claim 1, wherein step (e) further comprises extracting atleast a portion of the side stream with one or more extractive agents toyield an ethanol product stream with a reduced water content.
 16. Theprocess of claim 1, wherein the acetic acid is formed from methanol andcarbon monoxide, wherein each of the methanol, the carbon monoxide, andhydrogen for the hydrogenating step is derived from syngas, and whereinthe syngas is derived from a carbon source selected from the groupconsisting of natural gas, oil, petroleum, coal, biomass, andcombinations thereof.
 17. A process for producing ethanol, comprising:(a) providing a crude ethanol product comprising ethanol and ethylacetate; (b) separating at least a portion of the crude ethanol productin a first column to yield a first distillate comprising ethyl acetateand a first residue comprising ethanol; (c) hydrolyzing at least aportion of the first distillate in a hydrolysis unit to form ahydrolysis product comprising ethanol and acetic acid; (d) recovering anethanol side stream from at least a portion of the first residue in asecond column, wherein the ethanol side stream comprises 75 to 96 wt. %ethanol, less than 12 wt. % water, less than 1 wt. % acetic acid, andless than 5 wt. % ethyl acetate; and (e) reducing the water content ofthe ethanol side stream to yield an ethanol product stream with reducedwater content.
 18. A process for producing ethanol, comprising:hydrogenating acetic acid in a reactor in the presence of a catalyst toform a crude ethanol product; separating a portion of the crude ethanolproduct in a first column to yield a first distillate comprising ethylacetate and a first residue comprising ethanol, acetic acid and water,wherein at least 70% of the ethanol in the crude ethanol product that isfed to the first column is removed in the first residue; recycling atleast a portion of the first distillate to the reactor; separating atleast a portion of first residue in a second column to yield a sidestream comprising ethanol and a second residue comprising water andresidual acetic acid, wherein the side stream comprises 75 to 96 wt. %ethanol, less than 12 wt. % water, less than 1 wt. % acetic acid, andless than 5 wt. % ethyl acetate; and reducing the water content of theside stream to yield an ethanol product stream with reduced watercontent.
 19. The process of claim 18, wherein the first residue exitsthe first distillation column at a temperature from 70 to 155° C. 20.The process of claim 18, wherein the first residue comprises 10 to 75wt. % ethanol, 0.01 to 35 wt. % acetic acid, and 25 to 70 wt. % water.21. The process of claim 18, wherein the first distillate comprises 10to 85 wt. % ethyl acetate, 0.1 to 70 wt. % acetaldehyde, less than 55wt. % ethanol, and less than 20 wt. % water.
 22. The process of claim18, wherein the weight ratio of ethanol in the first residue to ethanolin the first distillate is at least 1:1.
 23. The process of claim 18,wherein the second column forms a second distillate comprising residualethyl acetate.
 24. The process of claim 18, wherein the ethanol productstream comprises less than 1 wt. % ethyl acetate.
 25. The process ofclaim 18, wherein the ethanol product stream comprises less than 3 wt. %water.
 26. The process of claim 18, further comprising separating atleast a portion of the side stream with a membrane into a permeatestream comprising water and a retentate stream comprising ethanol andless water than the at least a portion of the side stream.
 27. Theprocess of claim 18, further comprising extracting at least a portion ofthe side stream with one or more extractive agents to yield an ethanolproduct stream with a reduced water content.
 28. The process of claim18, wherein the acetic acid is formed from methanol and carbon monoxide,wherein each of the methanol, the carbon monoxide, and hydrogen for thehydrogenating step is derived from syngas, and wherein the syngas isderived from a carbon source selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.29. A process for producing ethanol, comprising: (a) providing a crudeethanol product; (b) separating a portion of the crude ethanol productin a first column to yield a first distillate comprising ethyl acetateand a first residue comprising ethanol, acetic acid and water, whereinat least 70% of the ethanol in the crude ethanol product that is fed tothe first column is removed in the first residue; (c) recycling at leasta portion of the first distillate to the reactor; (d) separating atleast a portion of first residue in a second column to yield a sidestream comprising ethanol and a second residue comprising water andresidual acetic acid, wherein the side stream comprises 75 to 96 wt. %ethanol, less than 12 wt. % water, less than 1 wt. % acetic acid, andless than 5 wt. % ethyl acetate; and (e) reducing the water content ofthe side stream to yield an ethanol product stream with reduced watercontent.
 30. A process for producing ethanol, comprising: (a)hydrogenating acetic acid in a reactor in the presence of a catalyst toform a crude ethanol product; (b) separating a portion of the crudeethanol product in a first column to yield a first distillate comprisingethyl acetate and a first residue comprising ethanol, acetic acid andwater, wherein at least 70% of the ethanol in the crude ethanol productthat is fed to the column is removed in the first residue; (c) recyclingat least a portion of the first distillate to the reactor; (d)separating at least a portion of first residue in a second column toyield a second distillate comprising residual ethyl acetate and a sidestream comprising ethanol, wherein the side stream comprises 75 to 96wt. % ethanol, less than 12 wt. % water, less than 1 wt. % acetic acid,and less than 5 wt. % ethyl acetate; and (e) reducing the water contentof the side stream to yield an ethanol product stream with reduced watercontent.
 31. A process for producing ethanol, comprising: providing acrude ethanol product comprising ethanol, ethyl acetate, water, andacetic acid; separating a portion of the crude ethanol product in afirst column to yield a first distillate comprising ethyl acetate and afirst residue comprising ethanol, acetic acid and water, wherein atleast 70% of the ethanol in the crude ethanol product that is fed to thecolumn is removed in the first residue; recycling at least a portion ofthe first distillate to the reactor; and separating at least a portionof first residue in a second column to yield a second distillatecomprising residual ethyl acetate and a side stream comprising ethanol,wherein the side stream comprises 75 to 96 wt. % ethanol, less than 12wt. % water, less than 1 wt. % acetic acid, and less than 5 wt. % ethylacetate; and (e) reducing the water content of the side stream to yieldan ethanol product stream with reduced water content.